1. Field of the Invention
This invention relates generally to a method for causing behavioral modifications in animals by altering retinal responses, and more particularly to a method for marking wind turbines so as to alter the motion smear blur that moving elements such as wind turbines create in avians and thereby cause the avians to alter their flight paths and avoid collisions with the wind turbines.
2. Description of Related Art
The development of wind power as a source for the generation of electricity has led to the establishment of xe2x80x9cwind farms,xe2x80x9d such as Altamont Pass, Calif. where thousands of wind turbines have been erected. While generally conceded to be environmentally safe, wind turbines have been reported to be hazardous to flying birds. The birds cannot effectively see the wind turbines when they are rotating, and they fly into the moving turbines and are maimed or killed. The present invention provides a principle for designing blade patterns to deter collisions of the birds with the wind turbines.
Motion smear is the degradation of the visibility of rapidly moving objects that results from the inability of the retina of the eye to process the high temporal frequencies of stimulation that result from high velocities of retinal-image motion. In the case of wind turbines, motion smear occurs primarily at the tips of the blades, making them deceptively transparent at high retinal-image velocities. Attempts to minimize motion smear must take into account its causes and attempts to reduce the temporal frequency of stimulation of the retinal. Anti-motion smear patterns are designed to do this by not repeating a pattern in one location on a turbine blade at the same location on any other blade. In a three-blade turbine, the temporal frequency of stimulation is thereby reduced by a factor of three.
To simulate turbines in a laboratory, a variable speed motor is used to spin an array of three blades with a diameter of 64 cm. The blades with anti-motion smear patterns are compared with blades that have no patterns or blades with patterns that are not staggered to reduce the temporal frequency of stimulation. Because this apparatus is relatively close to the subject""s eye, it is possible to simulate retinal-image velocities that would occur in a real environment with wind turbines having diameters of 20 m or more. In the method herein described, the subjects used were American kestrels (Falco sparverius). Each kestrel was anesthetized and electrodes were inserted under the eye lids in contact with the cornea to record the pattern electroretinogram (PERG) from the retina. The amplitude of the PERG in microvolts was the measure of pattern visibility.
Data show that anti-motion smear patterns produce a higher PERG amplitude, which translates into a higher pattern visibility at a given distance. For example, at a retinal velocity of 120 deg. of visual angle/sec, the most effective anti-motion smear patterns produce PERG amplitudes that were three times the amplitude of the blades with no patterns. A single, solid black blade, paired with two white blades, is one of the most visible stimulus, because it may stimulate a larger area of the retina than striped blades. Even though the anti-motion smear patterns are more visible at a distance of approximately 25 m than blank blades or blades with unstaggered, repeating patterns, as the bird gets closer to the blades, the retina is unable to process the progressively higher retinal-image velocities and all patterns rapidly lose visibility with decreasing distance.
It is an object of the present invention to provide a method and apparatus for reducing avian collisions with wind turbines.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.